Intervertebral implant with elastically deformable wedge

ABSTRACT

An intervertebral implant comprising a spacer for engaging between two spinous processes of two vertebrae of the spine. The spacer has two elements each presenting a first part suitable for being connected to a spinous process and bearing second parts opposite from the first part, the bearing second parts being situated facing each other. An elastically-compressible member is disposed between the bearing second parts. Links are provided which are distinct from the elastically-compressible member for linking together the two elements the link member being suitable for blocking translation movement of the two elements relative to each other when the two elements are driven apart from each other.

The present invention relates to an intervertebral implant including aspacer for being applied between two spinous processes of two vertebraeof the spine.

Well-known intervertebral implants comprise a spacer for insertingbetween the spinous processes which extend the posterior portions ofvertebrae in order to limit and control relative displacement of thevertebrae relative to one another. Such implants are generally installedon the spine of a patient suffering from a degenerative pathology of thespine in which the vertebrae run the risk of approaching one anotherand, for example, of compressing the roots of nerves. A first categoryof spacers has been devised that are entirely rigid and made as a singlepiece presenting two opposite ends suitable for being connectedrespectively to two contiguous spinous processes by link means. Thus,when the spine is extended, for example, the extent to which theposterior portions of two vertebrae can move towards each other islimited by the spacer against which the spinous processes come to bear;when the spine is bent forwards, the spinous processes are held relativeto each other by the link means. Nevertheless, such a rigid spacer doesnot reproduce accurately the real physiological conditions under whichrelative movement between vertebrae is limited. To mitigate thatproblem, a second category of spacers has been devised, made of materialthat is elastically deformable, thus making it possible to reproduce asaccurately as possible the conditions for controlled relativedisplacement of vertebrae during movements of the spine. As a result,the forces tending to push vertebrae apart increase as they move towardseach other.

Nevertheless, the elastically deformable materials used that aresuitable for being compressed in order to limit the extent to whichvertebrae can move towards each other deform in the longitudinaldirection in a manner that is too great compared with the displacementsof the vertebrae of a normal person.

A problem which arises and which the present invention seeks to solve isthus how to make a spacer that serves not only to control progressivemovement of vertebrae towards each other in order to limit suchmovement, but which also make it possible to prevent the spinousprocesses of the vertebrae from moving too far apart when they aredriven away from each other.

To this end, the present invention provides an intervertebral implantcomprising a spacer, said spacer comprising: two elements eachpresenting a first part suitable for being connected to a spinousprocess and a bearing second part opposite from said first part, thebearing second parts being situated facing each other;elastically-compressible means disposed between said bearing secondparts, said elastically-compressible means being suitable for beingcompressed by said bearing second parts when said two elements aredriven towards each other; and link means distinct from theelastically-compressible means for linking together said two elements,said link means being suitable for blocking translation movement of saidtwo elements relative to each other when said two elements are drivenapart from each other.

Thus, a characteristic of the intervertebral implant of the inventionlies in the way in which two elements secured to spinous processes arelinked together by link means suitable for preventing said elements frommoving in translation when they are moved away from each other, and byelastically-compressible means interposed between the second bearingparts which hold the elements spaced apart from each other. As a result,the spacer compresses longitudinally as the processes move towards eachother, with the force that the first parts exert thereon in order tokeep them apart being proportional to the extent to which theelastically-compressible means are compressed, and thus to the relativedisplacement of the processes relative to each other, and the spaceralso prevents the processes from moving further apart from each otheronce the elastically-compressible means have returned to their reststate in said implant.

It will be understood that the elastically-compressible means are usedonly during the compression stage, and that they perform their functionduring this stage only. During an extension stage, they are notsubjected to force, with only the link means being subjected to force,having the function of constituting a rigid block on displacement of thespinous processes in directions going apart from each other. This makesit possible to adjust separately the way in which the processes movetowards each other and apart from each other.

In a particularly advantageous embodiment of the invention, said linkmeans comprise at least one passageway passing through each of saidelements and opening out substantially on either side of said bearingsecond part. As a result, said elements can be held with their secondparts facing each other in a manner that is perfectly symmetrical oneither side of said bearing part. Preferably, said link means include aloop-forming continuous link, said continuous link presenting twoopposite first parts passing respectively through said two facingelements. Thus, the link is secured to the two elements in such a manneras to block them relative to each other when they move apart from eachother, so that the link becomes tensioned. Advantageously, the linkfollows the passageway passing through said elements.

In a preferred embodiment of the invention, each of said elementspresents at least a first portion and a second portion situatedsubstantially on either side of said bearing second part, the firstportion and the second portion of one of said elements being suitablefor pressing respectively against the second portion and the firstportion of the other element when said two elements are driven towardseach other so as to block them against moving in translation relative toeach other, the bearing second parts being suitable for compressing saidelastically-compressible means. Thus, according to this characteristic,the compressibility of the spacer is limited by the first and secondportions of the two elements. The spacer is thus capable of deformingbetween a rest or first position in which respectively the first andsecond portions of said elements are held spaced apart from each otherand in which the elastically-compressible means are lightly compressedbetween the bearing second parts and maintain the link means extended,and a stop or second position in which the first and second portions ofsaid elements are respectively in contact and in which the bearingsecond parts compress said elastically-compressible means.

Naturally, the compressibility of the elastically-compressible means,and the space between the first and second portions of said elements insaid rest position need to be adjusted in such a manner that the forceexerted by the elastically-compressible means on the facing bearingsecond parts when they are compressed is large when the first and secondportions come into contact. Thus, the spacer acts effectively as adamper without it being possible for the elements to come into contactviolently.

According to an advantageous characteristic, each of said elementspresents an anterior wall suitable for being applied against said spineand a posterior wall facing away from said anterior wall, and said firstportions and said second portions of said elements extend substantiallyparallel to one another, from said anterior walls to said posteriorwalls. As a result, as explained in greater detail below in the detaileddescription of an embodiment of the invention, the first and secondportions serve not only to block the elements one against the other, butalso make it easier to hold the elastically-compressible means.

Preferably, said bearing second parts of said two elements situatedfacing each other, and said respective first portions and secondportions together define substantially a volume opening out in theanterior and posterior walls of said two elements, saidelastically-compressible means extending in said volume. Thus, saidelastically-compressible means can be inserted between the elements ofthe spacer without impediment, when the elements are united together bysaid link means, either form the posterior walls or from the anteriorwalls.

Advantageously, said bearing second parts of said elements definerespective mean planes, said first portions of said elements extendingsaid bearing second parts substantially parallel to said mean planes,and said second portions of said elements extend said bearing secondparts substantially perpendicularly to said mean planes. Thus, saidfirst portion of one of the elements can come into contact with saidsecond portion of the other element which projects from the mean planeof the second bearing portion of the other element while its secondportion which projects from the mean plane of its bearing second partis, itself, suitable for coming into contact with said first portion ofthe other element. As a result, said volume is substantially defined bythe facing opposite bearing second parts and by said second portionslikewise situated facing each other.

In a particularly advantageous embodiment, said through passage passingthrough said elements opens out into said first and second portions andextends substantially perpendicularly to said mean planes of saidbearing second parts. As a result, the link means of the two elementswhose bearing second parts are placed facing each other exert a forcethat is substantially perpendicular to said mean plane on either side ofthe bearing second parts, thus enabling traction forces to be shared inbalanced manner between the elements of the spacer. This disposition isparticularly advantageous when, preferably, the loop-forming continuouslink is constituted by a continuous strip of flexible material.

When the link is flexible, it folds easily as soon as the spacerelements are moved towards each other by the spinous processes.

Preferably, said elements of the spacer are made of a rigid material sothat they do not deform under the stresses applied by the spinousprocesses and so as to compress the elastically-compressible means.Advantageously, said elastically-compressible means are formed as asingle piece of elastomer. Elastomers constitute a family ofelastically-compressible compounds presenting a low hysteresisthreshold, which is particularly advantageous for the spacer.

In a particularly advantageous embodiment, each of said first parts ofsaid elements further comprises connection means for connecting saidfirst parts to said spinous processes of said vertebrae. As explained inthe detailed description below, these connection means are generallyflexible. Nevertheless, rigid means could be used.

Other features and advantages of the invention will appear on readingthe following description of particular embodiments of the inventiongiven by way of non-limiting indication, and with reference to theaccompanying drawings, in which:

FIG. 1 is a diagrammatic perspective view of an intervertebral implantcomprising a spacer in accordance with the invention;

FIG. 2 is a diagrammatic cutaway view of the spacer shown in FIG. 1;

FIG. 3 is a diagrammatic view of the FIG. 1 implant seen from abovelooking along arrow III;

FIG. 4 is a diagrammatic vertical section view of the FIG. 3 spacer onplane IV; and

FIG. 5 is a diagrammatic side view of the FIG. 4 spacer seen lookingalong arrow V.

FIG. 1 shows an intervertebral implant 10 including a spacer 12 insertedbetween two spinous processes E1 and E2 of two respective vertebrae V1and V2, drawn in fine dashed lines. The spacer 12 comprises two elements14, 16 whose anterior walls 15 are disposed facing the vertebrae V1 andV2 of the spine, and whose posterior walls 17 face in the oppositedirection. The first element 14 presents a first part 18 connected tothe spinous process E1 and a second part 20 opposite the first part 18serving for bearing purposes and defining a mean plane P1. The secondelement 16 likewise presents a first part 22 which is connected to thespinous process E2 and an opposite-second part 24 for bearing purposesdefining a mean plane P2 and situated facing the bearing second part 20of the first element 14. The first parts 18 and 22 of each element 14and 16 are formed with a groove G with the spinous processes beingengaged between the side walls thereof, which processes bear against thebottoms 25 of the respective grooves G.

In addition, and in symmetrical manner, each element 14, 16 presents afirst portion 26, 28 and a second portion 30, 32 situated respectivelyfacing one another in pairs on either side of the bearing second parts20 and 24. The first portions 26 and 28 extend the edges of the bearingsecond portions 20 and 24 in slightly set-back manner, substantiallyparallel to the mean planes P1 and P2, and they extend from the anteriorwalls 15 to the posterior walls 17. The second portions 30 and 32 of theelements 16 and 14 serve to extend the other edges of the bearing secondparts 24 and 20 perpendicularly to the mean planes P2 and P1. Inaddition, the second portions 30 and 32 also extend from the anteriorwalls 15 to the posterior walls 17, substantially parallel to thecorresponding first portions 28 and 26. Thus, the spacer presents acentral volume V, defined by the second parts 20 and 24 of the twoelements 14 and 16 situated facing each other and by the respectivesecond portions 32, 30. The volume V opens out into the anterior andposterior walls 15 and 17 of the two element 14 and 16.

In addition, each of the second portions 30 and 32 of the elements 16and 14 is situated facing respective first portions 26 and 28 of theelements 14 and 16. As explained below, in a rest or first position, thefirst portions 26 and 28 are respectively spaced apart from each otherby a distance d.

The spacer 12 as shown in FIG. 1 includes link means constituted by athrough passage 34 passing through the two elements 14 and 16, and acontinuous link 36 forming a loop passing along said through passage 34so as to interconnect the two elements 14 and 16 of the spacer 12.Reference is made to FIGS. 2 and 4 in order to describe the link meansbetween the two elements 14 and 16 in greater detail, after describingin detail the implant that is shown in a cutaway view in FIG. 2 andwhich includes elastically-compressible means 38 disposed between thebearing second parts 20 and 24.

In FIG. 2, there can be seen the two elements 14 and 16 whose bearingsecond parts are placed facing each other, and with the second portions30 and 32 of the elements 16 and 14 disposed respectively facing thefirst portions 26 and 28 of the elements 14 and 16.

In addition, there can be seen a substantial fraction of the centralvolume V which is substantially in the form of a rectangularparallelepiped and in which the elastically-compressible means 38 arecontained completely. The elastically-compressible means 38 areconstituted by a single substantially rectangular block of biocompatibleelastomer material, e.g. of the silicone type. Said block presents afirst wall 40 and an opposite second wall 42 that are substantiallyparallel, the bearing second parts 20 and 24 of the elements 14 and 16bearing against these first and second walls 40 and 42 of said block. Itshould be emphasized that the elastically-compressible piece 38 is notpositively connected mechanically to the elements 14 and 16. Thesepieces merely bear against one another.

FIG. 2 also shows the passageway 34 in which the loop-forming continuouslink 36 extends in full, for the purpose of holding the elements 14 and16 together.

The passageway 34 is substantially rectangular in shape of width L thatis naturally smaller than the distance between the posterior andanterior walls 17 and 15 so that the first parts 18 and 22 of theelements 14 and 16 are secured to the bearing second portions 20 and 24,respectively.

Reference is made to FIG. 4 in order to describe in greater detail thepassageway 34 passing through the two elements 14 and 16, whichpassageway is followed by the loop-forming continuous link 36.

The passageway 34 passes through the elements 14 and 16 in the samerespective portions. It appears in the bottom 25 of the groove G of theelement 14 of the spacer 12 and passes through the spacer portions 46and 48 situated at the bases of the side walls of the groove G, openingout between the bearing second part 20 and the first portion 26 forspacer portion 46, and between the bearing second part 20 and the secondportion 32 for spacer portion 48. The passageway is also bordered by thesecond portion 32 as far as the element 16 where it opens out betweenthe bearing second part 24 and the first portion 28 in the spacer wall50 in a manner analogous to the spacer portion 46 of the element 14.Thereafter, it passes along the bottom 16 of the groove G so as to openout in spacer portion 52 and extend to the element 14 between thebearing second part 20 and the second portion 32, being bordered by thesecond portion 30. As a result, the passageway forms a loop goingthrough both elements 14 and 16.

It will be understood that the continuous link 36 which follows saidpart to form a loop enables the two elements 14 and 16 to be heldtogether.

FIG. 3 shows the spacer 12 seen from above, and in the figure there canbe seen the element 14 and the bottom 25 of the groove G along which thecontinuous link 36 constituting a flexible strip passes. The continuouslink 36 engages in the spacer portions 48 and 46 situated at the base ofthe groove G.

FIG. 5 shows the spacer 12 in side view, and in the figure there can beseen the element 14 and the element 16, with the continuous link 36being shown between the first portion 26 and the second portion 30thereof.

With the essential component elements of the spacer described above,there follows a description of how it is assembled and how it operates.

In a particularly advantageous implementation, the two elements 14 and16 are pressed against each other so that their first and secondportions are respectively in contact. Thereafter the continuous link 36is put into place by inserting a strip of flexible material around thethrough passage 34 and by connecting together the two ends of the stripby stitching so as to constitute the continuous link 36. The strip issewn in the bottom 25 of one of the grooves G which is the only locationavailable to a sewing device.

In addition, the strip is sewn in such a manner that the continuous link36 is relatively slack while the elements 14 and 16 are disposed oneagainst the other. As a result, as soon as the elements 14 and 16 aredriven apart from each other, the continuous link becomes tensioned andthe elements 14 and 16 are blocked relative to each other, with thefirst portions 26, 28 and the second portions 30, 32 being respectivelyspaced apart from one another by a distance d.

In this position where the elements 14 and 16 are spaced apart from eachother, the elastically-compressible means 38 constituted by a singleblock are inserted by force. As a result, the spacer 12 as shown inFIGS. 2 and 4 is in a rest, first position where the lightly compressedelastically-compressible means 38 exert force in opposite directions onthe bearing second parts 20 and 24 of the elements 14 and 16, tending tomove them apart from each other. Naturally, the elements 14 and 16 areheld together by the continuous link 36.

A spacer 12 is thus obtained in which the elastically-compressible meansare prestressed and in which the elements 14 and 16 are capable of beingmoved towards each other with a determined amount of force until thefirst and second portions 26, 28 and 30, 32 come respectively intocontact with one another, at which point the elements 14 and 16 areblocked one against the other.

Said determined force corresponds to the compressibility of theelastically-compressible means 38. It corresponds to the resistance thatis to be applied against moving the spinous processes towards eachother, and it is determined by selecting the type of elastomer and bythe extent to which it is prestressed.

In addition, since the first parts 18 and 22 of the elements 14 and 16are rigidly connected to the spinous processes, the extent to which theycan move apart from each other is limited solely by putting thecontinuous link 36 under tension. The bottoms 25 of the grooves G in thetwo elements 14 and 16 against which the continuous link 36 bears thenexerts oppositely-directed forces producing longitudinal tension in thestrip constituting said continuous link 36.

The force with which it is desired to hold the spinous processesrelative to each other as a function of the stresses to which they aresubjected can be determined by selecting a strip made of a material thatpresents determined elongation under stress.

Thus, the spacer of the invention presents the advantage of beingelastically deformable in compression and of being relatively rigid inextension since these two kinds of relative displacement are controlledby two distinct members.

1. An intervertebral implant comprising a spacer for placing between twospinous processes of two vertebrae of the spine, said spacer comprising:two elements each presenting a first part for being connected to aspinous process and a bearing second part opposite from said first part,said bearing second parts being situated facing each other;elastically-compressible means disposed between said bearing secondparts, said elastically-compressible means being compressed by saidbearing second parts when said two elements are driven towards eachother; and link means distinct from said elastically-compressible meansfor linking together said two elements, said link means blockingtranslation movement of said two elements relative to each other whensaid two elements are driven apart from each other.
 2. An intervertebralimplant according to claim 1, wherein said link means comprise at leastone passageway passing through each of said elements and opening outsubstantially on either side of said bearing second part.
 3. Anintervertebral implant according to claim 1, wherein said link meansinclude a loop-forming continuous link, said continuous link presentingtwo opposite first portions passing respectively through said two facingelements.
 4. An intervertebral implant according to claim 1, whereineach of said elements presents at least a first portion and a secondportion situated substantially on either side of said bearing secondpart said first portion and said second portion of one of said elementspressing respectively against the second portion and the first portionof the other element when said two elements are driven towards eachother so as to block them against moving in translation relative to eachother, the bearing second parts being suitable for compressing saidelastically-compressible means.
 5. An intervertebral implant accordingto claim 4, wherein each of said elements presents an anterior wallapplied against said spine and a posterior wall facing away from saidanterior wall said first portions and said second portions of saidelements extending substantially parallel to one another, from saidanterior walls to said posterior walls.
 6. An intervertebral implantaccording to claim 5, wherein said bearing second parts of said twoelements situated facing each other, and said respective first portionsand second portions together define substantially a volume opening outin said anterior and posterior walls of said two elements, saidelastically-compressible means extending in said volume.
 7. Anintervertebral implant according to claim, wherein said bearing secondparts of said elements define respective mean planes, and said firstportions of said elements extend said bearing second parts substantiallyparallel to said mean planes, and said second portions of said elementsextend said bearing second parts substantially perpendicularly to saidmean planes.
 8. An intervertebral implant according to claim 13, whereinsaid through passage passing through said elements opens out into saidfirst and second portions and extends substantially perpendicularly tosaid mean planes of said bearing second parts.
 9. An intervertebralimplant according to claim 3, wherein said loop-forming continuous linkis constituted by a continuous strip of flexible material.
 10. Anintervertebral implant according to claim 1, wherein said elements aremade of rigid material.
 11. An intervertebral implant according to claim1, wherein said elastically-compressible means are formed as a singlepiece of elastomer.
 12. An intervertebral implant according to claim 1,wherein each of said first parts of said elements (14, 16) furthercomprises connection means for connecting said first parts to saidspinous processes of said vertebrae.
 13. An intervertebral implantaccording to claim 7, wherein said bearing second parts of said elementsdefine respective mean planes, and said first portions of said elementsextend said bearing second parts substantially parallel to said meanplanes, and said second portions of said elements extend said bearingsecond parts substantially perpendicularly to said mean planes.